01 What sank in 1628
On 10 August 1628 the Vasa left central Stockholm on her maiden voyage. She sailed about thirteen hundred metres, fired a ceremonial salute, caught a light gust and heeled hard over. Water poured in through the lower gun ports, which were open, and she went to the bottom within minutes, in full view of the city.
That is where the familiar story ends and the interesting one begins. The ship stayed down for three hundred and thirty-three years. In 1956, after years of searching, the archaeologist Anders Franzén located the wreck; in April 1961 it was lifted to the surface. And what came up was not a scatter of frames: it was a ship.
02 The mollusc that does not live here
In practically every sea in the world there is a bivalve mollusc that bores into submerged wood, Teredo navalis, the shipworm. It is the reason ancient wrecks usually leave metal, ceramics and little else: the wood disappears.
The Baltic is an exception. It is almost enclosed, with a very narrow connection to the Atlantic, and it receives an enormous inflow of fresh water from rivers. The result is brackish water with a salinity too low for that mollusc to establish itself. Without shipworm, submerged wood lasts for centuries instead of decades.
And two more factors helped. The bottom water is cold and low in oxygen, which greatly slows bacterial decay. And the ship sank onto a bed of soft mud that quickly covered the lower hull, creating an oxygen-free environment around it. Three conditions at once, none of them intended.
It was not preserved by anyone's skill: it was preserved because a mollusc lacks the salt it needs to live here.
03 Raising it was the easy part
Wood that has spent three centuries soaked falls apart on drying: it loses the water holding its structure and shrinks and cracks. To prevent that, the ship and its objects were treated with polyethylene glycol, a substance that replaces the water inside the wood. Smaller pieces were immersed in steel tanks with a solution heated to 60 °C, the concentration raised day by day to 40–45 per cent.
The problem did not end there, and this is the part almost never told. Since the summer of 2000 the ship has suffered an acid attack: sulphur accumulated in the wood over the centuries underwater oxidises, combines with iron and moisture and surfaces as yellow and white deposits, iron sulphate salts, some with a pH below 2.
That is why the hall is so carefully climate-controlled: relative humidity around the hull is held between 51 and 59 per cent and the temperature around 18–20 °C. Polyethylene glycol is hygroscopic, absorbing and releasing moisture, so any swing moves water inside the wood and worsens the process. The ship is not simply on display: it is in permanent treatment.
04 How to look at it
One piece of advice that changes the visit: do not start at the stern, where everyone gathers. Start underneath, walking the full circuit of the hull on the lowest level of the hall. From there you see the underwater body, the run of the planking and the keel — exactly the part that was buried in the mud and the part best preserved.
And once upstairs, look for one specific thing: the difference in colour between the dark, almost black wood and the pale pieces. The dark is original; the pale is generally replacement. Taking in that proportion at a glance is the best way to grasp the scale of what that saltless sea allowed to reach us.
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